|
I can see the muscles that make up my face, my skull, and my own brain. So, now I can take you on that journey into my ear in a way that’s never been possible before. This time we can fly straight through my eardrum. We're inside my head and at last I can show you what we’ve come here to see. On the right, it’s my eardrum again, but now we’re looking at it from the back. And attached to the middle of it is what I want to show you. It’s a bone. Though it’s towering above us, it’s actually tiny, about the size of a grain of rice. It’s the first in a chain of three bones which transfer the vibrations of my eardrum to receptors in my cochlea. They are the smallest bones in my body and they are perfectly engineered to perform their task, yet these bones will reveal how evolution has transformed us because they were once something completely different. Let me take you back even before birth, and the bones will tell us their story: a fetus in the womb, just 12 weeks old and it’s only a few centimeters long, it would fit in an eggcup.
---Deep inside its head, its ear bones are forming. Now let’s look at younger and younger fetuses: 8 weeks, 7 weeks, 6 weeks. We are actually witnessing something amazing because at certain times in this early development our human embryo betrays the shapes of the embryos of some of our distant prehuman ancestors. In other words, what we are looking at now is like the embryo of a creature we evolved from millions of years ago. It’s just as if we are journeying back in time virtually rewinding evolution to show episodes in the history of life.
---If we use the magnetic scanner, incredible details are revealed. We can see right through the skin of the brain and the spinal cord beginning to form, and the beginnings of an eye behind the emerging hand. Like some of the creatures that preceded us on the evolutionary tree, it has a curved spine and what might be a tail. And those amazing ear bones we saw earlier are taking shape on the outside of the head. The cells that will make them are located here, tiny grooves almost hidden behind that hand.
words and expressions
tower:tower vi.
（常与above, up连用）高耸；屹立
cochlea:A spiral-shaped cavity of the inner ear that resembles a snail shell and contains nerve endings essential for hearing.
耳蜗：内耳的螺旋形内腔，像蜗壳，有主要用于听的神经末梢
fetus: In human beings, the unborn young from the end of the eighth week after conception to the moment of birth, as distinguished from the earlier embryo.
胎儿：人类从开始怀孕的第八个星期到出生这一期间的有别于更早期的胚胎的幼儿
spinal cord :The thick, whitish cord of nerve tissue that extends from the medulla oblongata down through the spinal column and from which the spinal nerves branch off to various parts of the body.
脊髓：从延髓开始沿脊柱延伸的粘稠、白色、索状的神经组织，由脊髓开始脊椎神经分叉伸向身体各个部位
|